The present invention relates to an ink-jet recording head of an ink jet recording apparatus and, more particularly, to the structure of an ink reservoir for supplying ink to an ink cavity which generates pressure for use in ejecting ink droplets.
An ink-jet recording head is a device which records an image on recording paper by pressurizing an ink cavity filled with ink so as to jet ink from a nozzle orifice (or an opening). As inexpensive color ink-jet printer have recently become more popular, a demand has grown for a high-density nozzle orifice and a compact ink-jet head. To meet this demand, a spacer which constitutes a space for pressurizing ink to eject ink droplets, or an ink flow path such as a so-called ink cavity, is formed by anisotropic etching. In the anisotropic etching operation, a silicon monocrystalline substrate is etched using an alkaline liquid, so that the difference in etch rates in the crystallographic axis is utilized.
FIGS. 15A and 15B show one example of an ink-jet recording head which uses a spacer S formed by anisotropically etching a silicon monocrystalline substrate. A plurality of substantially-rectangular ink cavities A are formed in the spacer S on constant pitches in the direction of a shorter side of the cavity. In the direction of a longer side of each ink cavity A, the ink cavity A is connected at one end to an ink reservoir C via an ink supply port B. A nozzle orifice D for ejecting ink is formed in the other end of each ink cavity A.
A resilient plate E is fitted to one side of the spacer S of the recording head that has flow paths such as the ink cavities A formed therein. Further, a nozzle plate F having the nozzle orifices D formed therein is fitted to the other side of the spacer S.
A lower electrode H which is to serve as a common electrode, piezoelectric films J formed so as to correspond to the ink cavities A, and upper electrodes K which are formed so as to correspond to the ink cavities A and to serve as segment electrodes, are formed in that order on the surface of the resilient plate E.
A drive signal is fed to these electrodes from outside via an electrically conductive pattern (not shown) formed on the surface of the resilient plate E. A terminal for receiving a flexible cable which connects the electrically conductive pattern to an external drive circuit, is usually provided along one end of the recording head.
In contrast, in the ink-jet recording head having the previously-described structure, ink other than the ink ejected from the nozzle orifices D reversely flows to the ink reservoir C from the ink supply ports B if the plurality of ink cavities A are pressurized. If a large quantity of ink reversely flows to the ink reservoir C, the pressure of the ink reservoir C will increase, thereby resulting in the ink flowing into the unpressurized ink cavities A. As a result, ink droplets will be ejected from the nozzle orifices D of the unpressurized ink cavities A. Such interaction arising between adjacent ink reservoirs (cross-stroke) is not a desirable phenomenon in the ink-jet recording head.
It is necessary to prevent the pressure of the ink reservoir C from increasing in order to eliminate such a problem. To this end, a thin portion M which is likely to be deformed as a result of an increase in the pressure of the ink reservoir C due to the reverse flow of ink from the ink cavity A, is formed in the resilient plate E so as to correspond to the ink reservoir C.
In filling an ink-jet head with ink by, e.g., replacing a used ink tank with a new one, it is necessary to forcibly introduce the ink to the flow path of the recording head from the ink tank by exerting a strong negative pressure on the ink tank through the nozzle orifice D.
The area of the resilient plate corresponding to the ink reservoir C, i.e., the thin portion M, is deformed as a result of exertion of the negative pressure generated when the ink is introduced. As a result, the lower electrode H, the piezoelectric film J, and the upper electrode K stacked on the resilient plate E also experience large stress, and hence they are significantly deformed, which in turn results in the upper electrode K becoming apt to break.
The present invention has been conceived in light of the aforementioned drawback in the conventional one.
An object of the present invention is to provide an ink-jet recording head capable of preventing break in a line while reducing interaction to as small as possible.
To solve the previously-described problem, the present invention provides an ink-jet recording head comprising: a nozzle plate having a plurality of nozzle orifices formed therein for ejecting ink in the form of an ink droplet; a spacer made comprising, substantially-rectangular ink cavities for pressurizing ink which are respectively connected to the nozzle orifices and are arrayed on constant pitches in the direction of a shorter side of the ink cavity, ink supply ports connected to the respective ink cavities for supplying ink, and an ink reservoir connected to the ink supply ports for supplying ink to the plurality of ink cavities, wherein the nozzle plate seal one surface of the spacer; a resilient plate sealing the other side of the spacer and brings about variations in the pressure of the ink cavity; a piezoelectric substance formed on the surface of the resilient plate; upper electrodes formed so as to respectively correspond to the ink cavities in order to apply a signal to the piezoelectric substance; a thin portion which is elastically deformable when being subjected to the ink reversely flowed from the ink cavity and is formed at least in either a portion of the nozzle plate being opposite to the ink reservoir or in an interior of the ink reservoir.
Even if ink reversely flows into an ink reservoir from an ink cavity, a portion other than a resilient plate is deformed. The resilient plate is not deformed, and therefore electrodes formed on the resilient plate are not deformed. Further, another element is deformed to absorb pressure as a result of reverse flow from the ink cavity.